The present invention relates to a swing-type actuator such as an actuator for magnetic disk drives, and more particularly to a swing-type actuator with a thin, reinforced movable coil and capable of swinging a function member such as a magnetic head along a circular course.
Conventionally, the positioning of a magnetic head on a recording track of a magnetic disk, etc. is conducted by a swing-type or rotation-type actuator as shown in FIGS. 7, 8. In both figures, a yoke 1 is fixedly provided with permanent magnets 2, and a pair of yokes 1 are assembled by supports 3 such that different magnetic poles of the permanent magnets 2 are opposite each other via a magnetic gap 4 to form a magnetic circuit. 5 represents an arm having one end to which a flat movable coil 6 is fixed, and the other end to which a magnetic head (not shown) is fixed. The arm 5 is arranged such that the movable coil 6 located in the magnetic gap 4 can swing around a shaft 7. When an operation signal is supplied to the movable coil 6, a magnetic force generated from the movable coil 6 according to Fleming's left hand rule functions as an attraction force or a repulsion force to each permanent magnet 2, so that the arm 5 is rotated around the shaft 7. As a result, a magnetic head (not shown) fixed to a tip end of the arm 5 is positioned on a desired magnetic track of a magnetic disk (not shown). The direction of the rotation of the arm 5 can be changed by inverting the direction of current applied to the movable coil 6.
In the above conventional actuator for magnetic disk drives, the movable coil 6 is usually fixed to the arm 5 by an adhesive. However, the fixing of the movable coil 6 by an adhesive is sometimes troublesome, failing to provide accurate positioning of the movable coil 6. In addition, handling of terminals of the movable coil 6 is complicated, lowering the efficiency of assembling the arm 5. Since there is increasingly higher demand for miniaturization and reduction in thickness of magnetic disk drives, it is necessary to improve the positioning accuracy of the movable coil 6, and the productivity and reliability of fixing the movable coil 6 to the arm 5. In this sense, the conventional arms fail to satisfy these requirements.
Attempts have been made to integrally fix a movable coil to an arm by a resin molding (for instance, Japanese Utility Model Laid-Open No. 60-159566 and U.S. Pat. No. 4,855,853). In such a structure, the movable coil can be easily fixed, and the thickness of the movable coil can be significantly reduced. Accordingly, such a structure is advantageous for miniaturizing actuators. Also, a magnetic circuit member is constituted by fixing a permanent magnet to only one of the yokes, thereby making the actuator thinner.
However, the conventional resin molding fails to show sufficient mechanical strength and sufficient adhesion to the arm and a movable coil. Further, since the movable coil is molded together with a hold member, a resin layer having a relatively large thickness is formed on each side of the movable coil. As a result, the actuator is relatively thick, requiring the large magnetic gap. Therefore, the magnetic properties of the permanent magnet cannot be fully utilized, leading to the poor performance of the actuator.